Descendants of American president Martin Van Buren, Adeline and Augusta Van Buren were born into a life of privilege that assured them the safe and respectable existences of society women. But with America on the brink of war, the sisters ditched their gilded cages for a cross-country adventure they hoped would change their beloved nation for the better.

By July 1916, America was readying to enter World War I, and 32-year-old Augusta and 26-year-old Adeline were eager to do their part as motorcycling military dispatch riders, transporting crucial communications to the front line. Women were flat-out barred from combat duty in the U.S., but as bikers with thousands of hours logged on the roaring vehicles, the Van Burens felt they were uniquely qualified for such arduous and dangerous missions. And they were determined to prove it. By the end of their journey, they would become the first women to travel across the country on two solo motorcycles.

Fittingly, Addie and Gussie—as they preferred to be called—set forth on Independence Day. From Brooklyn’s Sheepshead Bay racetrack, they headed to the Lincoln Highway, which ran from Times Square in Manhattan to Lincoln Park in San Francisco. They had top-of-the-line bikes: $275 Indian Power Plus motorcycles that boasted Firestone “non-skid” tires and gas headlights that would allow them to barrel through the darkest nights. They had an indomitable spirit. They had each other. And they’d need all the courage and resources they could muster for this daunting endeavor.

“There were no road maps west of the Mississippi,” their great-nephew and historian Robert Van Buren explained to the Worcester, Massachusetts Telegram of the sisters’ epic journey. “The roads were just cow passes, dirt trails, wagon trails, things like that.” The Lincoln Highway was far from the paved superhighways of today. Heavy rain proved a major problem, wiping out roads and throwing the Van Burens off-course and off their bikes. “They had no helmets. They just had goggles with a leather cap and leathers on. They were really exposed to the elements,” Van Buren said. “They had a tough time.” Yet weather and murky maps weren’t their only obstacles.

Just west of Chicago, the motorcycling mavens were pulled over by police—not for the way they were driving but for the way they were dressed. Though women’s fashion was shifting from corsets to more comfy attire, dresses were still the norm. In some states it was actually illegal for women to wear pants. So the Van Burens’ military-style leggings and leather riding breeches got them arrested again and again by confounded cops. Between arrests and weather delays, the sisters’ one-month journey stretched into two.

By August, Addie and Gussie reached Colorado’s Rocky Mountains and earned their first record, becoming the first women to reach the 14,109-foot summit of Pike’s Peak by motorized vehicle. Running behind schedule, the sisters abandoned their plan to ride north through Wyoming, favoring a more direct path through the Rockies. Unfortunately, relentless rain transformed the mountains’ dirt paths to sucking mud that mercilessly trapped their tires. Exhausted, freezing, and filthy from their fruitless efforts to free their wheels, the dejected duo was forced to abandon their bikes and seek out help on foot. Hours and miles later, the sisters slid out of the darkness upon the small mining town of Gilman, Colorado. They were quite the sight to the awed miners: two angel-faced ladies draped in leather and caked in mud.

The miners offered them rest and food, then helped the sisters free their bikes. But another brush with disaster came 100 miles west of Salt Lake City, where the winds had whisked away the desert’s path, and the pair was woefully low on water. Thankfully, their luck held up again: A prospector came along who not only had a horse-drawn cart packed with supplies, but also a keen sense of direction to get them back on their way.

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Exhausted and elated, Addie and Gussie Van Buren reached San Francisco at long last on September 2, having traveled 5500 miles, and completed their journey on September 8 after arriving in Los Angeles. And still, they pressed on, traveling down to the Mexican border and Tijuana.

Their remarkable ride earned headlines, but much of the media coverage disappointed. Leading motorcycle magazines focused on the bikes, not the bikers. Others ignored the purpose and historical import of their journey, publishing puff pieces about the ladies’ curious “vacation.” Worse yet, The Denver Post accused the sisters of exploiting World War I to abandon their duties at home to “display their feminine counters in nifty khaki and leather uniforms.” But most vexing, the U.S. government was unmoved, and rejected the Van Burens’ application for dispatch service.

Following their cross-country adventure, the boundary-busting sisters pursued new passions. In a time when female lawyers were unheard of, Addie earned her law degree at prestigious New York University. Meanwhile, Gussie became a pilot, flying in Amelia Earhart’s Ninety-Nines, an international organization dedicated to creating a supportive environment and opportunities for aviatrixes. With these accomplishments, each sister added credence to Gussie’s famous maxim, “Woman can, if she will.”

While their journey didn’t deliver the immediate impact the sisters had hoped for, today they are remembered as pioneers for women and motorcyclists alike. Addie and Gussie’s courageous spirit and intense independence is celebrated by descendants and admirers who have kept their legacy alive through cross-country rides that traced their path on the trip’s 90th and 100th anniversaries. Plus, both the Sturgis Motorcycle Museum’s Hall of Fame in South Dakota and the AMA Motorcycle Hall of Fame of Ohio have posthumously inducted the Van Burens as esteemed members.

Both Addie and Gussie enjoyed full lives with careers that thrilled them, and family that loved and still rally around them, decades after their deaths at ages 59 and 75 respectively. In their time, these headstrong and hearty sisters witnessed the passing of the 19th Amendment that gave women the vote. They cheered the female patriots who rushed into the workforce as World War II demanded. They relished in a world that was changing to meet them, the industrious, rebellious, and brave Van Burens.